Fireproof design method of orthogonal engineering bamboo-concrete composite floor

Abstract

The application discloses a kind of orthogonal engineering bamboo-concrete composite floor fireproof design method, it includes: selecting the cross-sectional dimension of composite floor, using gamma-method to calculate the stiffness and stress distribution of composite floor, checking deformation and strength under normal temperature, determine the cross-sectional dimension that meets normal temperature design requirement;Determine the fire resistance limit design requirement and the most unfavorable load combination effect design value of composite floor under fire;Using gamma-method to calculate the stress distribution of the remaining cross section of composite floor after carbonization, the fire resistance limit of composite floor is obtained by iteration calculation;Compare whether the fire resistance limit calculation value of composite floor is not less than the fire resistance limit design value, if meet, then determine the cross-sectional dimension of composite floor;If not satisfied, then increase the number of engineering bamboo lamella in composite floor;Repeat the above steps until the fire resistance limit of composite floor meets the design requirement, determine the cross-sectional dimension of composite floor.The application forms a kind of scientific, accurate, effective orthogonal engineering bamboo-concrete composite floor fireproof design method.

Description

TECHNICAL FIELD

[0001] The application relates to a fireproof design method of a building structure, in particular to a fireproof design method of an orthogonal engineering bamboo-concrete composite floor. BACKGROUND

[0002] Bamboo is a renewable and green material, which will help achieve the development goal of carbon neutralization and carbon peak in China. Research shows that bamboo has high tensile strength and high strength-to-weight ratio, and can be used to replace wood in building structures. After 3 to 9 layers of engineering bamboo such as laminated bamboo and reconstituted bamboo are orthogonally assembled and pressed into orthogonal engineering bamboo boards using structural adhesives, the strength and stiffness in two directions are similar, and the overall stress performance is good, which can fully utilize the performance of engineering bamboo and can be widely used in floor or wall boards. Due to the small elastic modulus of engineering bamboo, the deformation control is usually used in the design of large-span floor, and the material strength of engineering bamboo cannot be fully utilized. To solve this problem, the orthogonal engineering bamboo board is connected to the concrete board through shear connection to form an orthogonal engineering bamboo-concrete composite floor, which can significantly improve the bearing capacity and deformation performance of the orthogonal engineering bamboo board.

[0003] Fire is one of the main disasters threatening the public and social development, which can cause great loss to the national economy and human beings. Engineering bamboo is a combustible material, and the orthogonal engineering bamboo floor needs scientific fireproof design to ensure the fire safety performance of the engineering bamboo structure.

[0004] However, since the orthogonal engineering bamboo-concrete composite floor is composed of cross-grain boards, parallel-grain boards and concrete layers, there is slippage between different boards, and the influence of slippage needs to be considered when calculating the bearing capacity of the composite floor, and the engineering bamboo board carbonizes after being exposed to fire, and the bearing mechanism of the composite floor is complex during fire. At present, there is still a lack of fireproof design method for the composite floor considering the influence of slippage deformation between the orthogonal engineering bamboo board and the concrete board. SUMMARY

[0005] In view of the above defects and deficiencies in the prior art, the application aims to provide a scientific, accurate and effective fireproof design method for the orthogonal engineering bamboo-concrete composite floor, which provides technical support for the fire safety of the composite floor.

[0006] To achieve the above-mentioned purpose, the application adopts the following technical solutions:

[0007] A fireproof design method for an orthogonal engineering bamboo-concrete composite floor, comprising the following steps:

[0008] Step S1: Select the cross-sectional size of the composite floor, calculate the stiffness and stress distribution of the composite floor by using the γ-method, check the deformation and strength at normal temperature, and determine the cross-sectional size that meets the design requirements at normal temperature; in the selection process, the cross-sectional size is determined according to the checking results; if the checking results do not meet the design requirements at normal temperature, the number of layers of the orthogonal engineering bamboo is increased, otherwise the thickness of the orthogonal engineering bamboo is reduced;

[0009] Step S2: Determine the fire resistance limit design requirements and the most unfavorable load combination effect design value of the composite floor under fire.

[0010] Step S3: Calculate the stress distribution of the remaining cross-section of the composite floor after carbonization by using the γ-method, and obtain the fire resistance limit of the composite floor through iterative calculation.

[0011] Step S4: Compare whether the calculated value of the fire resistance limit of the composite floor is not less than the design value of the fire resistance limit, if it is satisfied, the cross-sectional size of the composite floor is determined, if it is not satisfied, the number of layers of the engineering bamboo in the composite floor is increased, and the process jumps to step S3.

[0012] The calculation of the stiffness and stress distribution of the composite floor by using the γ-method in step S1 and step S3 specifically includes:

[0013] (a) Number the concrete layer and each layer of the orthogonal engineering bamboo floor from top to bottom as 1-n; wherein the number of the concrete layer is 1, and the number of each layer of the orthogonal engineering bamboo floor is 2-n;

[0014] (b) Calculate the combination effect coefficient of the concrete layer:

[0015]

[0016] In the formula, γ1 is the combination effect coefficient of the concrete layer, E c A c is the axial stiffness of the concrete layer, K is the stiffness of the shear connection between the concrete layer and the orthogonal engineering bamboo layer, s is the spacing of the shear connection arrangement, and l is the span of the floor.

[0017] (c) Calculate the combination effect coefficient of the orthogonal engineering bamboo layer:

[0018]

[0019] In the formula, γ i is the combination effect coefficient of the i-th layer of the orthogonal engineering bamboo, the combination effect coefficient of the intermediate layer is 1, E i A i is the axial stiffness of the i-th layer of the orthogonal engineering bamboo, G R is the rolling shear modulus of the orthogonal engineering bamboo layer, is the thickness of the i-th layer of the parallel layer plate on the side of the middle layer plate, and b is the width of the parallel layer plate. Among them, the span direction l of the orthogonal engineering bamboo floor is along the grain direction of the parallel layer plate; the width b of the parallel layer plate is perpendicular to the grain direction of the parallel layer plate.

[0020] The selection rule of the middle layer plate is: for a three-layer orthogonal engineering bamboo floor, the uppermost parallel layer plate is taken as the middle layer plate; for an orthogonal engineering bamboo floor with more than three layers, the most adjacent parallel layer plate above the geometric center of the orthogonal engineering bamboo floor is taken as the middle layer plate. For example, for a seven-layer orthogonal engineering bamboo floor, the second layer of the parallel layer plate is taken as the middle layer plate.

[0021] (d) Calculate the distance conversion value between the centroid of each parallel layer plate and the total section centroid, which is expressed as:

[0022]

[0023] In the formula, the subscripts i, j, and k are all layer plate numbers, wherein: when i is 1, the corresponding layer plate is a concrete layer, and when i is other values in the value range, it represents the corresponding parallel layer plate; a i is the distance between the i-th layer plate centroid and the total section centroid, y i is the distance between the i-th layer plate centroid and the centroid of the middle layer plate, and n is the total number of all layers, including the total number of parallel layer plates and concrete layers, and excluding the cross layer plate.

[0024] (e) Calculate the effective flexural rigidity of the orthogonal engineering bamboo-concrete composite floor:

[0025]

[0026] In the formula, (EI) ef is the effective flexural rigidity of the composite floor, E i I i is the flexural rigidity of the i-th layer plate, wherein n is the total number of all layers, including the total number of parallel layer plates and concrete layers, and excluding the cross layer plate.

[0027] (f) Check the deformation of the orthogonal engineering bamboo-concrete composite floor:

[0028]

[0029] In the formula, δ is the deformation of the composite floor, [δ] is the deformation limit value of the composite floor, and M is the bending moment of the calculation section. The deformation δ of the composite floor is less than the deformation limit value [δ] of the composite floor, indicating that the orthogonal engineering bamboo-concrete composite floor meets the corresponding checking condition.

[0030] (g) checking the strength of the orthogonal engineered bamboo-concrete composite floor slab, wherein each layer of the slab is checked respectively, and the expression is:

[0031]

[0032] when γ i E i a i ≤ 0.5E i h i ,

[0033]

[0034] when γ i E i a i > 0.5E i h i ,

[0035]

[0036] Grain direction layer:

[0037] Cross grain direction layer:

[0038]

[0039] wherein f c , f t are the compressive and tensile strength of the orthogonal engineered bamboo layer respectively, f v , f vb are the shear strength and rolling shear strength of the orthogonal engineered bamboo layer respectively, F is the ultimate load of the shear connection; V is the shear force of the calculation section; σ it is the normal stress at the top of the i-th grain direction layer, σ ib is the normal stress at the bottom of the i-th grain direction layer, τ i is the shear stress of the i-th layer (grain direction layer or cross grain direction layer); m is the total number of grain direction layers above the shear surface of the corresponding layer and the concrete layer. The bending moment M and the shear force V of the calculation section are the checking conditions, including the design requirements of step S1 and the fire resistance limit design value of step S3.

[0040] The shear surface is taken at the upper edge of the layer when calculating the shear stress of the grain direction layer, and the shear surface is taken at the middle of the cross grain direction layer when calculating the shear stress of the cross grain direction layer. The shear stress of the concrete layer is not calculated, and the shear stress is 0.

[0041] The fire resistance limit design requirement of the composite floor is determined according to the requirement of the standard, and the most unfavorable load combination effect design value under fire should consider the load (action) that can occur simultaneously on the structure under fire and is determined according to accidental combination.

[0042] The step S3 comprises:

[0043] (a) assuming that the fire resistance limit of the composite floor is t, determining the remaining cross section of the composite floor after charring:

[0044] According to the charring speed of the engineering bamboo and the fire-affected mode of the composite floor, the charring depth of the orthogonal engineering bamboo at the time t when the fire-affected time is t is determined, and then the remaining cross section size of the orthogonal engineering bamboo after the fire-affected is determined. The charring depth of the orthogonal engineering bamboo is:

[0045] d ef =β n t+C d

[0046] In the formula, β n is the nominal charring speed of the engineering bamboo, C d is the corner effect value, which is 7mm for the glued bamboo component and 5mm for the reconstituted bamboo component. The thickness of the original composite floor minus the charring depth is the height of the remaining cross section, and the width of the remaining cross section does not change with charring. The fire-affected mode of the composite floor is the bottom surface.

[0047] (b) the stress distribution of the remaining cross section is calculated by using the gamma-method calculation method, and the bending and shearing bearing capacity of the composite floor at the time t when the fire-affected is determined, if the bending or shearing bearing capacity is equal to the most unfavorable load combination effect design value under fire, the fire resistance limit of the composite floor is t, otherwise, the fire resistance limit is taken as t+0.01 and jump to step a for the next iteration. In each iteration process, as long as one of the bending or shearing bearing capacity is equal to the corresponding most unfavorable load combination effect design value under fire, the iteration can be stopped.

[0048] In the process of calculating the stress distribution of the remaining cross section, if the residual layer board of the bottom layer of the composite floor is a cross-grain layer board, the cross-grain layer board only participates in the charring depth calculation and does not participate in the gamma-method calculation.

[0049] The increase of the number of the layer boards of the engineering bamboo in the composite floor refers to the simultaneous increase of a layer of cross-grain and longitudinal-grain layer boards.

[0050] The present application has the following advantages:

[0051] The present application provides a fireproof design method of the orthogonal engineering bamboo-concrete composite floor, which is simple and efficient in calculation, and the method considers the combination of the orthogonal engineering bamboo layer board and the concrete composite floor in a reasonable way, and has high calculation precision.

[0052] Additional aspects and advantages of the present application will be set forth in part in the following description, will become apparent from the following description, or will be learned through practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0053] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, taken in conjunction with the accompanying drawings, in which:

[0054] Figure 1 A flowchart of a fireproof design method of an orthogonal engineered bamboo-concrete composite floor according to an embodiment of the present application.

[0055] Figure 2 A schematic diagram of an orthogonal engineered bamboo-concrete composite floor according to an embodiment of the present application.

[0056] In the drawings:

[0057] 1 - concrete slab (1st layer of slab), 2 - orthogonal engineered bamboo slab in grain direction (2nd layer of slab), 3 - orthogonal engineered bamboo slab in grain direction (3rd layer of slab), 4 - orthogonal engineered bamboo slab in cross grain direction, 5 - self-tapping screw. DETAILED DESCRIPTION

[0058] The present application will be described in detail below with specific embodiments. Figure 2 Take the orthogonal engineered bamboo-concrete composite floor shown in the figure as an example. An office building uses the orthogonal engineered bamboo-concrete composite floor, the thickness of the slab in grain direction is 34 mm, the thickness of the slab in cross grain direction is 30 mm, the thickness of the concrete slab is 60 mm, the width of the composite floor is 1000 mm, the span is 4500 mm, the elastic modulus of the engineered bamboo is 8600 MPa, the rolling shear modulus is 60 MPa, the tensile strength is 32.2 MPa, the compressive strength is 21.4 MPa, the shear strength is 2.6 MPa, the rolling shear strength is 2.0 MPa. The form of shear connection is double-row self-tapping screw, the interval is 180 mm, the stiffness of shear connection is 100 kN / mm, the ultimate load of shear connection is 40 kN. The elastic modulus of concrete is 30000 MPa. The bottom surface of the composite floor is subjected to fire.

[0059] According to the above operation, the calculation steps of the fire resistance are as follows: Figure 1

[0060] Step S1: Select the number of layers of the orthogonal engineered bamboo slab as 3 layers, and number the concrete layer and the orthogonal engineered bamboo slab in grain direction from top to bottom as 1-3.

[0061] The self-weight q of the composite floor and decoration, etc. G = 3.2 kN / m​2 , floor live load q Q = 2.0 kN / m 2

[0062] Load fundamental combination effect design value: q = 7.16 kN / m 2 , M = 18.12 kN.m, V = 16.11 kN; Load quasi-permanent combination effect design value: q k = 5.20 kN / m 2 , M k = 13.16 kN.m

[0063] Calculate the combination effect coefficient of the concrete layer:

[0064]

[0065] Calculate the combination effect coefficient of the orthotropic engineered bamboo layer:

[0066] γ2 = 1.0,

[0067] Calculate the distance between the centroid of each layer and the centroid of the total section:

[0068]

[0069] a2 = 5.8 mm, a3 = 69.8 mm

[0070] Calculate the effective flexural rigidity of the orthotropic engineered bamboo-concrete composite floor slab:

[0071]

[0072] Check the deformation of the orthotropic engineered bamboo-concrete composite floor slab:

[0073]

[0074] Check the strength of the orthotropic engineered bamboo-concrete composite floor slab:

[0075]

[0076]

[0077]

[0078]

[0079] The inequalities of each check are all true, and the three-layer orthotropic engineered bamboo slab meets the design requirements at room temperature.

[0080] Step S2: The fire resistance limit design requirement of the composite floor slab is determined as 0.75h according to the standard requirement.

[0081] The most unfavorable load combination effect design value under fire shall consider the load (action) that may simultaneously occur on the structure under fire determined by accidental combination:

[0082] Self-weight q of the combined floor and decoration, etc. G = 3.4 kN / m 2 Floor live load q Q = 2.0 kN / m 2

[0083] Accidental combination effect design value q under fire T = 4.62 kN / m 2 M T = 11.69 kN.m.

[0084] Step S2: assuming that the fire resistance limit of the combined floor is t, the remaining cross section of the combined floor after charring is determined.

[0085] According to the charring speed of the engineering bamboo and the fire receiving mode of the combined floor, the charring depth of the orthogonal engineering bamboo plate at the time t when the fire receiving time is t is determined as:

[0086] d ef = β n t + C d

[0087] The stress distribution of the remaining cross section is calculated according to the γ-method calculation method, and the bearing capacity of the combined floor at the time t when the fire is received is determined, if the bearing capacity is equal to the most unfavorable load combination effect design value under fire, the fire resistance limit of the combined floor is t, otherwise, the fire resistance limit is taken as t+0.01, the bearing capacity of the remaining cross section after the fire is recalculated, until the bearing capacity after the fire is equal to the most unfavorable load combination effect design value under fire, and the fire resistance limit of the combined floor is iteratively calculated to be 1.3h.

[0088] The cross section size meets the design requirements.

[0089] The above detailed the preferred embodiments of the present application. It should be understood that those skilled in the art can make many modifications and changes without creative labor according to the concept of the present application. Therefore, any technical solution that can be obtained by logical analysis, reasoning or limited experiment by those skilled in the art on the basis of the prior art according to the concept of the present application shall be within the protection scope determined by the claims.

Claims

1. A method for fireproof design of an orthogonal engineered bamboo-concrete composite floor slab, characterized in that, The method comprises the following steps: Step S1: select the cross-sectional size of the composite floor, calculate the stiffness and stress distribution of the composite floor by using the finite element method, check the deformation and strength at normal temperature, and determine the cross-sectional size that meets the design requirements at normal temperature; Step S1: select the cross-sectional size of the composite floor, calculate the stiffness and stress distribution of the composite floor by using the finite element method, check the deformation and strength at normal temperature, and determine the cross-sectional size that meets the design requirements at normal temperature; Step S2: determining the fire resistance limit design requirement and the most unfavorable load combination effect design value of the composite floor under fire; Step S3: Use —Calculate the stress distribution of the remaining cross section of the composite floor slab after carbonization, and obtain the fire resistance limit of the composite floor slab through iterative calculation; Step S4: comparing whether the fire resistance limit calculated value of the composite floor is not less than the fire resistance limit design value, if yes, determining the cross-sectional size of the composite floor; If not, increasing the number of the layer plates of the engineered bamboo in the composite floor, and jumping to step S3; The step S3 comprises: (a) assuming that the fire resistance limit of the composite floor is t, determining the remaining cross section after carbonization of the composite floor: According to the carbonization speed of the engineered bamboo and the fire exposure mode of the composite floor, the carbonization depth of the orthogonal engineered bamboo plate at the time t is determined, and then the remaining cross-sectional size of the orthogonal engineered bamboo plate after fire exposure is determined; the carbonization depth of the orthogonal engineered bamboo is: ； wherein is the nominal charring rate of the engineered bamboo material, is the corner effect value, taken as 7 mm for glued bamboo elements and 5 mm for reconstituted bamboo elements; the thickness of the original composite floor minus the charring depth is the height of the remaining cross section; (b) using The stress distribution of the remaining cross section is calculated by the method, and the flexural and shear bearing capacities of the composite floor at time t under fire are determined. If the flexural or shear bearing capacity is equal to the design value of the most unfavorable load combination effect under fire, the fire resistance of the composite floor is t, otherwise, the fire resistance is taken as t+0.01 and jump to step a for the next iteration.

2. The orthogonal engineered bamboo-concrete composite floor slab fireproof design method according to claim 1, characterized in that, The method comprises the following steps: The rigidity and stress distribution of the combined floor are calculated by the method, and the deformation and strength at normal temperature are checked, specifically including: (a) the concrete layer and each parallel layer plate of the orthogonal engineered bamboo floor are numbered from top to bottom as 1~n; wherein the number of the concrete layer is 1, and the number of the parallel layer plate of the orthogonal engineered bamboo floor is 2~n; (b) calculating the combination effect coefficient of the concrete layer: ； In the formula, is the combined effect coefficient of the concrete layer, is the axial stiffness of the concrete layer, K is the stiffness of the shear connection between the concrete layer and the orthotropic engineered bamboo layer, s is the spacing of the shear connection arrangement, and l is the span of the floor. (c) calculating the combination effect coefficient of the parallel layer of the orthogonal engineered bamboo: ； wherein, is the combined effect coefficient of the i-th layer of the parallel layer board, the combined effect coefficient of the intermediate layer board is 1, is the axial stiffness of the i-th layer of the parallel layer board, G R is the rolling shear modulus of the orthogonal engineered bamboo layer board, is the thickness of the i-th layer of the parallel layer board on the side of the intermediate layer board, b is the width of the parallel layer board; (d) calculating the distance conversion value between the centroid of each layer plate and the centroid of the total cross section, and the expression is: ； wherein is the distance between the centroid of the i-th layer and the overall cross-sectional centroid, is the distance between the centroid of the i-th layer and the centroid of the intermediate layer, n is the total number of layers, including the total number of layers of the concrete layers and the layers of the laminates, and the subscripts i, j, k are the numbers of the layers, wherein: i is 1, the corresponding layer is a concrete layer, and i is other values in the value range, indicating the corresponding layers of the laminates. (e) calculating the effective flexural rigidity of the orthogonal engineered bamboo-concrete composite floor: ； wherein is the effective flexural rigidity of the composite floor, is the flexural rigidity of the i-th floor slab; (f) checking the deformation of the orthogonal engineered bamboo-concrete composite floor: ； wherein is the deformation of the composite floor, is the deformation limit of the composite floor, M is the bending moment of the calculation section; (g) checking the strength of the orthogonal engineered bamboo-concrete composite floor: ； When time, ； When time, ； Grain parallel ply: ; Cross-laminated timber: ; ； wherein, , respectively are the compressive and tensile strength of the orthogonal engineered bamboo layer board, , respectively are the shear strength and rolling shear strength of the orthogonal engineered bamboo layer board, F is the ultimate load of the shear connection; V is the shear force of the calculation section; is the normal stress at the top of the i-th layer of the parallel layer board, is the normal stress at the bottom of the i-th layer of the parallel layer board, is the shear stress of the i-th layer of the layer board; m is the total number of the parallel layer board and the concrete layer above the shear surface of the corresponding layer board.

3. The orthogonal engineered bamboo-concrete composite floor slab fireproof design method according to claim 1, characterized in that, The increase of the number of the layer plates of the engineered bamboo in the composite floor refers to the simultaneous increase of one layer of the cross grain and parallel layer plate.

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